1. Field of the Invention
The present invention relates to a droplet-ejecting apparatus such as an inkjet-recording apparatus. It also relates to a piezoelectric element for use in the droplet-ejecting apparatus, a method of preparing the same, and a droplet-ejecting head using the same.
2. Description of the Related Art
Inkjet-recording apparatus is one of the conventional droplet-ejecting apparatuses for printing by ejecting droplets from multiple nozzles onto a recording medium such as paper, and has various advantages such as smaller size, low price, and lower noise, and is commercially available. In particular, a recording apparatus using a piezoelectric method that ejects an ink droplet by changing the pressure in a pressure chamber by using a piezoelectric element, and a recording apparatus using a thermal method that ejects an ink droplet by expanding ink by heat energy have many advantages such as high printing speed and high-resolution image.
Piezoelectric bodies used in the piezoelectric method occupy a greater area relative to those of ejection elements (heating units) used in the thermal method, and thus, it is difficult to increase the density and the length of the recording head. For that reason, a configuration of the piezoelectric elements arranged in a grid pattern is now being studied. However, the piezoelectric bodies for use in the piezoelectric method are normally composed of sintered materials, and sintered materials conventionally used did not have sufficiently high piezoelectric property, and as a result, a greater element area is needed.
In contrast, piezoelectric bodies formed by deposition methods such as vapor growth methods and liquid phase growth methods are superior in crystallinity and orientation and have a higher piezoelectric property compared with sintered materials, and thus, reduction in area and increase in density and length are expected. The formation methods of piezoelectric bodies by the deposition methods are highly suitable for common semiconductor processes and large-area electronic device processes, in which Si substrates and glass substrates are used.
On the other hand, the piezoelectric element in an inkjet-recording head demands a greater displacement of a diaphram for increase in the ink drop volume, and thus, a thick piezoelectric film having a thickness of 5,000 Å or more is needed.
As described, for example, in JP-A No. 2003-154646, piezoelectric elements generally have a sandwich structure wherein the piezoelectric body is held between a pair of top and bottom electrodes, and have the following problems:
First, in the piezoelectric body area including the piezoelectric body active area (active area where recording liquid is displaced in a pressure chamber), the area other than the piezoelectric body active area also operates and consumes wasteful energy. When a piezoelectric body is wired as it is in the sandwich structure wherein the piezoelectric body is held between the top and bottom electrodes, capacitance according to the wiring length is added, causing a problem of variation and increase in the capacitance for each piezoelectric body. In particular, increase in the capacitance of piezoelectric bodies that have a high dielectric constant of several hundreds or more is significant. In addition, the variation in the capacitance of each piezoelectric body leads to fluctuation in the energy applied to the piezoelectric body, so that it is difficult to maintain the uniform ink ejecting property-from the entire head. The fluctuation in the capacitance of each bit is a serious problem, particularly in piezoelectric elements having a two-dimensional configuration wherein piezoelectric bodies are arranged in a grid pattern for increase in density and length.
In addition, there are the following problems, in forming such a thick piezoelectric film by a vapor- or liquid-phase growth method:
First, when a piezoelectric body is deposited on an area having an amorphous underlayer, the perovskite-phase crystallization temperature needed for piezoelectric property (temperature needed to form the perovskite crystal phase) increases by approximately 50 to 100° C.
Further, when a piezoelectric body is deposited in an area having an amorphous underlayer, amorphous phase and mixed crystals of perovskite and pyrochlore phases are often formed, so that this process is not suitable for forming a uniform piezoelectric body.
Further, the piezoelectric body layer is occasionally separated or cracked in the area having an amorphous underlayer.
The phenomena described above tend to become marked with increase in thickness of the piezoelectric body.